There is substantial interest in reducing the weight of parts used to manufacture vehicles such as automobiles, trucks, airplanes and boats for the purpose of improving fuel economy. One approach to reducing the weight of parts is to use light weight/high strength aluminum alloys to manufacture such parts.
The yield strength of parts made of supersaturated, heat treatable aluminum alloys may be increased by aging the parts over a substantial period of time. Waiting for natural aging to occur is generally not economically feasible in manufacturing processes due to the long period of time required, and further, will not result in the part reaching peak strength. Some parts are included in assemblies that are painted and baked in a paint oven, but the time and temperature of the paint bake oven may be inadequate to fully strengthen the parts.
Aging may be accelerated by heating the parts in a process referred to as “artificial aging.” For example, parts made of AA6111 series aluminum in the T4 temper may be artificially aged by heating the parts and can result in a doubling of the yield strength of the parts. Typically, it is not possible to form a given part after artificial aging due to the associated increase in yield strength and decrease in formability. Hence, it is desirable to manufacture such parts by forming when the parts are in the more formable T4 temper and subsequently artificially aging the parts to achieve the desired strength. Furthermore, the parts when processed in this manner will have less elastic recovery after forming. Pre-forming operations may include drawing, stretching, piercing, trimming, bending, extruding, forging or hydro-forming operations.
One problem with artificial aging is that it is impossible to determine by visual inspection whether the parts were subjected to the artificial aging process. A tensile test may be used to verify the yield stress of a part but a tensile test is destructive to the part. While a time consuming and relatively expensive hardness test could be used to test for artificial aging, these types of hardness tests may not be an accurate predictor of yield stress.
Structural beams, such as pillars, roof rails, frame parts, and the like once assembled to a vehicle may also be located in inaccessible areas that cannot be readily checked for yield strength. The yield strength of such parts may be critical to vehicle durability and/or vehicle quality. If it is determined that such structural parts lack the specified strength characteristics after the fact, costly corrective actions would be required such as replacing the part or adding a strengthening patch.
This disclosure is directed to solving the above problems and other problems as summarized below.